1. Field of the Invention
The present invention relates to a membrane-electrode assembly for a fuel cell, a method of manufacturing the same, and a fuel cell system including the same.
2. Description of the Related Art
A fuel cell is a power generation system which produces electrical energy through an electrochemical redox reaction of an oxidant and hydrogen in a hydrocarbon-based material such as methanol, ethanol, or natural gas.
Such a fuel cell is a clean energy alternative that can replace fossil fuels. A typical fuel cell includes a stack composed of unit cells which produces various ranges of power.
Representative exemplary fuel cells include a polymer electrolyte membrane fuel cell (PEMFC) and a direct oxidation fuel cell (DOFC). The direct oxidation fuel cell includes a direct methanol fuel cell that uses methanol as a fuel.
The polymer electrolyte fuel cell has relatively high energy density, and high power output, but needs a fuel reforming processor for reforming methane, methanol, natural gas, and the like in order to produce a hydrogen-rich gas as the fuel gas.
In contrast, a direct oxidation fuel cell has lower energy density than that of the polymer electrolyte fuel cell, but it does not need a fuel reforming processor and can operate at room temperature due to its relatively low operation temperature.
In a fuel cell, the stack that generates electricity includes unit cells that are stacked in multiple layers, and each of the unit cells is composed of a membrane-electrode assembly (MEA) and one or more separators (also referred to as bipolar plates). The membrane-electrode assembly has an anode (also referred to as a fuel electrode or an oxidation electrode), a cathode (also referred to as an air electrode or a reduction electrode), and a polymer electrolyte membrane between the anode and the cathode.
A fuel is supplied to the anode and absorbed in a catalyst thereof, and the fuel is oxidized to produce protons and electrons. The electrons are transferred to the cathode via an external circuit, and the protons are transferred to the cathode through the polymer electrolyte membrane. An oxidant is supplied to the cathode, and the oxidant, protons, and electrons are reacted on a catalyst at the cathode to produce heat along with water.